1. Field of the Invention
The present invention relates to a braking system of an automobile, and more particularly to a braking system having a variably exhausting pump unit which enables the braking system not only to perform a braking function but to utilize the energy of hydraulic pressure which is generated during the braking and which may be lost without the unit.
2. The Prior Arts
It is well-known in the art that a brake is a system for stopping or decelerating an automobile being driven. The brake system performs the braking function in such a manner that it transforms the kinetic energy of a traveling automobile into a heat energy by means of a mechanical friction apparatus and radiates the frictional heat into the atmosphere.
Recently, the automobile is generally equipped with various systems for improving its traveling stability, such as an anti-lock braking system (ABS) and a traction control system (TCS). The ABS is a system for ensuring a strong and stable braking capability by properly controling the hydraulic pressure of the brake when the automobile is braked on slippery or uneven ground. The TCS is a system for preventing the driving wheels from slipping when the automobile is rapidly accelerated to start on slippery ground by applying proper braking pressure to the driving wheels even when the brake pedal is not stepped on.
FIG. 1 shows a schematic hydraulic circuit diagram of a conventional braking system. As shown, the conventional braking system includes a brake pedal 10 arranged under a driver's seat and connected to a master cylinder 11 which transfers an external force applied to the brake pedal 10. A brake booster 12 is arranged between the brake pedal 10 and the master cylinder 11 to boost the braking power. One end of a first fluid path 20 is connected to the master cylinder 11, while a first solenoid valve 30 for controling the flow of fluid is disposed at the other end of the first fluid path 20. The first solenoid valve 30 is connected to a second fluid path 21 which extends up to a braking section 70 and is connected through a second solenoid valve 31 to a third fluid path 22 branching off from the first fluid path 20. A pump 41 driven by a motor 40, a check valve 50, and a tank 90 are provided between the third fluid path 22 and the second solenoid valve 31. A speed sensor 81 for sensing the braked state of a wheel 60 is provided in the braking section 70, and the conventional braking system further includes an electronic control unit (ECU) 80 which controls the first solenoid valve 30, the second solenoid valve 31, and the motor 40, according to signals from the speed sensor 81.
In operating the conventional braking system as described above, when a driver steps on the brake pedal 10, the master cylinder 11 generates a hydraulic pressure, which is transferred through the first solenoid valve 30 to the braking section 70 The hydraulic pressure enables a piston installed in a caliper 62 to push a pad toward a disc 61, thereby performing the braking function (see FIG. 2). In this case, the fluid or oil supplied from the master cylinder 11 through the first fluid path 20 to the third fluid path 22 is interrupted by the check valve 50, and the second solenoid valve 31 also is blocked off. Therefore, the oil is not supplied through the second fluid path 21.
While the braking force is being applied to the wheel 60, the speed sensor 81 disposed at one side of the wheel 60 senses if the wheel 60 slips. When a slip of the wheel 60 is sensed by the speed sensor 81, the ECU 80 closes the first solenoid valve 30 to interrupt the supply of oil into the braking section 70, opening the second solenoid valve 31 to make the oil having been supplied in the braking section 70 be retrieved into the tank 90 through the second fluid path 21 and the second solenoid valve 31, thereby decreasing the braking force applied to the wheel 60.
The decrease of braking force by the above process eliminates the slip of the wheel 60, and then the speed sensor 81 again senses the elimination of slip of the wheel 60 and reports it to the ECU 80. According to the signals from the speed sensor 81, the ECU 80 opens the first solenoid valve 30, closes the second solenoid valve 31, and at the same time orders the operation of the motor 40. Then, the pump 41 pumps the oil in the tank 90 to supply the braking section 70 through the third fluid path 22 and the first solenoid valve 30, thereby performing the braking operation. By repeating the process as above, the ABS performs its function. The reference numeral 100 not described above designates the differential gear.
FIG. 2 schematically shows an entire construction of a disc brake employed in the conventional braking system, referring to which the operation of the disc brake will be described hereinbelow.
When a driver steps on the brake pedal 10, the hydraulic pressure generated by the master cylinder 11 is transferred through an introduction port 121 to a cylinder 120. This hydraulic pressure makes a piston 130 compress an inner pad 140 against a disc 160 in an instant, and at the same time the hydraulic pressure remaining in the cylinder 120 makes caliper 110 move rightward by means of a sliding member (not shown), so as to compress an outer pad 150 against the disc 160, thereby performing the braking function. When the brake pedal 10 is released, the piston 130 is restored to its original position due to the elastic force of a seal within groove 131. Then, the disc 160, the inner pad 140, and the outer pad 150 are spaced again at a predetermined distance.
However, in the conventional braking system described above, the heat energy produced by the friction between the disc and the pads in the course of braking the car is discharged untouched into the atmosphere to disappear, which is not an efficient use of energy. Further, the frictional heat shortens the life of the elements in the braking system.
Moreover, the conventional braking system is also problematic in that its construction is very complicated because it requires individual systems for performing an anti-lock braking function and a traction control function, respectively.